The present invention relates to an improved precess for the production of aromatic nitriles from nuclearly halogenated aromatic hydrocarbons and to catalytic compositions for carrying out the process.
Nitriles, organic cyanides, are useful organic compounds becuase of their high reactivity. Nitriles are readily hydrolyzed with acids or alkalies to form various useful carboxylic acid amides, acids and salts. For example, terephalonitrile is an intermediate for condensation polymers based on terephthalic acid, and benzoic acid, a derivative of benzonitrile, is a widely used commercial chemical. Many of the nitrile products are, for example, benzonitrile, useful solvents.
Nitriles have been synthesized from carboxylic acid ammonium salts or amides by distillation with a strong dehydrating agent, such as phosphorus pentoxide. However, since such processes involve the use of relatively expensive raw materials, the nitrile products are not produced on a competitive basis. Nitriles may be produced by passing carboxylic acids or esters in a vapor phase with ammonia over a bed of alumina maintained at a temperature of about 500.degree. C. This process also involves relatively expensive starting materials and has an additional detriment of low yield. The commercial production of nitriles has generally been carried out using low cost organic halides reacted, for example, with potassium cyanide under pressure, in liquid phase in dilute alcohol solutions, to convert the halide to a nitrile. The major shortcomings of such processes is that the yields are usually poor, because of competing reactions and the usual presence of malodorous isonitriles in the product. Nitriles are also produced commerically by reacting organic halides with hydrogen cyanide in vapor phase reactions at temperatures of 650.degree. C. or above, or at lesser temperatures, e.g., about 480.degree. C. to about 650.degree. C., in the presence of metal or metal oxide catalysts. Although such vapor phase reactions have attained a fair conversion of halide to cyanide, the yield and selectivity have not reached more than a barely satisfactory level.
More recently, it has been proposed in the literature to produce nitriles by the replacement of halides on aryl compounds with cyanide ions using palladium salt catalysts. The reactions are carried out in a dipolar, aprotic solvent, such as hexamethylphosphoric triamide, tetramethylurea, N,N-dimethylformamide, N,N-dimethylacetamide, propylene carbonate or N-mthoylpyrrolidone. Examples of such reactions are given by K. Takagi, Bull. Chem. Soc. Jap., Vol. 48, pages 3298 (1975) and K. Takagi, et al, Bull. Chem. Soc. Jap., Vol. 49, page 3177 (1976).